A comparative study of electrocatalytic hydrogen evolution by iron complexes of corrole and porphyrin from acetic acid and water

Article abstract of DOI:10.1007/s11243-019-00307-5

Iron complexes of corrole and porphyrin bearing electron-withdrawing meso-C₆F₅ groups had been used for the electrocatalytic evolution of hydrogen. In neutral buffer solution, evolution of hydrogen turnover frequency (TOF) values for iron corrole and iron porphyrin were 274 and 233?h^?1 at an overpotential of 838?mV versus standard hydrogen electrode (SHE). The corresponding TOF values had dropped sharply to 19.79?h^?1 and 14.36?h^?1 in acetic acid media at an overpotential of 942?mV versus SHE. Interestingly, hydrogen evolution catalyzed by Fe(III) porphyrin was mainly via an Fe(I)-H intermediate, while a higher valent Fe(III)-H intermediate was observed for Fe(IV) corrole.

Full text of DOI:10.1007/s11243-019-00307-5

Transition Metal Chemistry
https://doi.org/10.1007/s11243-019-00307-5
A comparative study of electrocatalytic hydrogen evolution by iron
complexes of corrole and porphyrin from acetic acid and water
Ya‑Qian Zhong1 · Md. Sahadat Hossain1 · Ying Chen1 · Qi‑Hang Fan1 · Shu‑Zhong Zhan1 · Hai‑Yang Liu1
Received: 20 November 2018 / Accepted: 23 January 2019
© Springer Nature Switzerland AG 2019
Abstract
Iron complexes of corrole and porphyrin bearing electron-withdrawing meso-C6F5 groups had been used for the electro-
catalytic evolution of hydrogen. In neutral bufer solution, evolution of hydrogen turnover frequency (TOF) values for iron
corrole and iron porphyrin were 274 and 233 h−1 at an overpotential of 838 mV versus standard hydrogen electrode (SHE).
The corresponding TOF values had dropped sharply to 19.79 h−1 and 14.36 h−1 in acetic acid media at an overpotential of
942 mV versus SHE. Interestingly, hydrogen evolution catalyzed by Fe(III) porphyrin was mainly via an Fe(I)-H intermedi-
ate, while a higher valent Fe(III)-H intermediate was observed for Fe(IV) corrole.
Introduction
activity. In the electrocatalytic HER process, the metal
center is the active site by participating in the formation
of metal–hydride species and the redox center in the multi-
electron reduction reaction [11]. Metalloporphyrins have
been well documented for their ability to generate H2 elec-
trochemically [12] or photochemically [13]. Corrole is a
kind of porphyrin analogue having a direct pyrrole–pyrrole
linkage and an extra inner N–H proton. Recently, cobalt
corroles were reported to be efcient catalysts for hydro-
gen evolution in 0.5 M sulfuric acid aqueous solutions or in
acetonitrile solutions by using trifuoroacetic acid (TFA) as
the proton source [14, 15]. Experimental evidence showed
that there was a remarkable enhancement in the catalytic
HER ability of the metal corrole with the increase in the
number of periphery fuorine atoms [16]. It is been demon-
strated that strong electron-withdrawing substituents, such
as meso-pentafluorophenyl groups, can lower the HER
overpotential of metal corrole catalysts signifcantly [15].
Similar trends were also observed for a series of transition
metal porphyrin HER catalysts. 5,10,15,20-tetra(pentafuo
rophenyl)porphyrin (TPFP) is a typical electron-defcient
porphyrin [17], whose nickel [18], copper and cobalt [19]
complexes as well as the free base [20] have been used to
catalyze hydrogen production. In contrast, the metal com-
plexes with 5,10,15-tris(pentafuorophenyl)corrole (TPFC)
are less explored in electrochemical HER, only Co-TPFC
[15] and Cu-TPFC [21] have been tested in HER; Cu-TPFC
degraded rapidly in acidic solution through an oxida-
tive dimerization process. As corrole has a narrower cav-
ity than porphyrin and can stabilize higher oxidation state
Hydrogen is an excellent clean energy source because it is
renewable and environmentally friendly. To obtain hydro-
gen efciently, people have attempted diferent approaches
such as splitting water by electrocatalytic [1] and photocata-
lytic methods [2]. Decomposing water by electrochemical
reduction is a convenient way to store electrical energy as
chemical energy through generating H2 [3, 4]. Hydrogenases
catalyze the reversible reduction of protons with high TOF
values up to 9000 s−1 in living system [5]. However, it is
difcult to deploy hydrogenases in non-natural environ-
ments, limiting their practical applications [6]. Platinum is
very active in electrocatalytic hydrogen production [7], but
limited by its low natural abundance and high cost. Other
transition metals are cheaper and can be used for more sus-
tainable catalytic hydrogen evolution.
In fact, many complexes with earth-abundant transition
metals such as cobalt [8], copper [9], iron [10] have already
been explored as hydrogen evolution reaction (HER) cat-
alysts and some of them show promising electrocatalytic
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-019-00307-5) contains
supplementary material, which is available to authorized users.
* Hai-Yang Liu
chhyliu@scut.edu.cn
1
Department of Chemistry, The Key Laboratory of Fuel Cell
Technology of Guangdong Province, South China University
of Technology, Guangzhou 510641, China
Vol.:(0123456789)
1 3

Transition Metal Chemistry
transition metals, metallocorroles may achieve superior
HER activity than metalloporphyrins with a lower overpo-
tenial. Also, it is well known, electrolyzing water to pro-
duce hydrogen will change the water to weakly alkaline
around the working electrode. Previous reports showed iron
β-pyrrole-brominated 5,10,15-tris(pentafuorophenyl)cor-
role (Fe(TPFCBr8)) exhibited good catalytic performance
in alkaline media [22]. Although Fe(TPFC) is an excellent
catalyst for cyclopropanation of styrene [23], it has not been
reported to be applied in HER. Here, we wish to report the
electrocatalytic HER activity of FeIV(TPFC)Cl (Scheme 1);
FeIII(TPFP)Cl was also investigated for comparison. The
results showed that FeIV(TPFC)Cl exhibited better HER
performance both in acid media and neutral water media.
Furthermore, FeIV(TPFC)Cl and FeIII(TPFP)Cl displayed
diferent pathways in their HER processes. For FeIV(TPFC)
Cl, hydrogen was evolved from the bimolecular homogeni-
zation of the Fe(III)-H intermediate, while the combination
of metal–hydride Fe(I)-H intermediate and a proton was
the main pathway for hydrogen evolution by FeIII(TPFP)Cl.
Also, under the same conditions, FeIV(TPFC)Cl produced
twice more hydrogen than FeIII(TPFP)Cl.
U-3010 spectrophotometer. X-ray photoelectron spectros-
copy (XPS) spectra were recorded with an Axis Ultra DLD
spectrophotometer.
Cyclic voltammograms were obtained with a CHI-660E
electrochemical analyzer using a three-electrode system in
which a glassy carbon electrode (1 mm in diameter) was the
working electrode, saturated Ag/AgCl (in phosphate bufer
solution) and Ag/AgNO3 (in DMF solution) were the refer-
ence electrodes and a platinum wire was the auxiliary elec-
trode. The ferrocenium(+)/ferrocene (Fc+/Fc) couple was
used as an internal standard in DMF solution. The support-
ing electrolytes were 0.1 M KCl and 0.1 M [(n-Bu)4N]ClO4
(TBAP). Controlled potential electrolysis (CPE) experiments
were conducted using a sealed glass double-compartment
cell blocked of by a glass frit. The working compartment
was flled with 40 mL of 0.25 M bufer solution (acetonitrile/
water=2:3 in volume as solvent) containing 0.1 M KCl as
the supporting electrolyte, a glassy carbon plate as work-
ing electrode and an Ag/AgCl reference electrode, while the
auxiliary compartment was flled the same solution and just
ftted with a platinum gauze electrode. Both compartments
were purged with nitrogen for no less than 1 h. On adding
the complex to the working compartment, the CPE experi-
ment was conducted. After electrolysis for 60 min, CH4 was
added to the reactor as an internal standard, and the gas
mixture in the working compartment was evaluated using an
Agilent Technologies 7890A gas chromatograph.
Experimental
Materials and methods
All reagents were purchased from commercial sources and
were high-grade in purity. Pyrrole was freshly distilled
prior to use. High resolution mass spectra were recorded
with a Bruker maxis impact mass spectrometer installed
Preparation of the complexes
Preparation of TPFC and TPFP
1
with an electrospray ionization (ESI) source. H NMR
TPFC was synthesized by the reactions of pyrrole with
pentafuorobenzaldehyde according to a reported method
[24]. UV–Vis (CH2Cl2) λmax/nm (log ε): 409 (4.65), 562
and 19 F NMR spectra were recorded with a Bruker Avance
III 400 MHz spectrometer in CDCl3 (δ = 7.26 ppm) solu-
tion. UV–visible spectra were recorded with a Hitachi
1
(3.82), 606 (3.71). H NMR (400 MHz, CDCl3, δ, ppm):
Scheme 1 Chemical formula of
F
Fe(TPFC)Cl and Fe(TPFP)Cl
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
N
N
N
N
Cl
Fe
F
F
F
F
F
F
F
F
F
F
N Cl N
Fe
F
F
N
N
F
F
F
F
F
Fe(TPFP)Cl
Fe(TPFC)Cl
1 3

Transition Metal Chemistry
9.07 (d, 2H), 8.80 (d, 2H), 8.63 (d, 2H), 8.57 (d, 2H). 19F
NMR (376 MHz, CDCl3, δ, ppm): − 137.80 (dd, J =23.5,
7.6 Hz), −152.82 (t, J=20.9 Hz), −161.95 (d, J=8.6 Hz).
ESI-HRMS, calcd for C37H11F15N4: 797.0817, found for
C37H11F15N4: 797.0816.
product was purified by column chromatography using
DCM/MeOH (98/2). After washing the product with dilute
hydrochloric acid (7%), the dark solid was obtained by
recrystallizing from DCM/hexane solution. Yield 10.2 mg
(46%). UV–Vis (CH2Cl2) λmax/nm (log ε): 345 (4.29),
416 (4.53), 507 (3.65), 636 (3.18). ESI-HRMS, calcd
for C44H8F20FeN4: 1027.9774, found for C44H8F20FeN4:
1027.9766.
TPFP was also synthesized by the reactions of pyrrole
with pentafluorobenzaldehyde (different molar ratios)
according to the reported method [25]. UV–Vis (CH2Cl2)
λmax/nm (log ε): 413 (5.39), 507 (4.24), 584 (3.76). 1H NMR
(400 MHz, CDCl3, δ, ppm): 8.95 (s, 8H), −2.88 (s, 2H). 19
F
NMR (376 MHz, CDCl3, δ, ppm): − 136.50 (dd, J =23.5,
8.0 Hz), − 151.23 (t, J = 20.8 Hz), − 161.33 (dt, J = 24.7,
8.6 Hz). ESI-HRMS, calcd for C44H10F20N4: 975.0659,
found for C44H10F20N4: 975.0654.
Results and discussion
Oxidation state of iron complexes
Generally, Fe(III) corrole or Fe(II) porphyrin is easily oxi-
dized to form diiron(IV) μ-oxo biscorrole or diiron(III)
μ-oxo bisporphyrin during the preparation process. The
dimer could be converted to monomer under the acidic con-
dition. Thus, the target monomer products FeIV(TPFC)Cl
and FeIII(TPFP)Cl were obtained by washing their dichlo-
romethane solution with dilute hydrochloric acid. The
dimer-monomer changes could be traced by UV–Vis spec-
tra (Fig. 1). The characteristic dimer peak around 550 nm
disappeared upon washing the dichloromethane solution
of the complex with hydrochloric acid. This is consistent
with the literature report [26]. To further check the oxida-
tion state of iron in these complexes, we have carried out an
XPS analysis of FeIV(TPFC)Cl and FeIII(TPFP)Cl (Fig. 2).
XPS spectrum of FeIII(TPFP)Cl shows two peaks at binding
energy 710.2 eV (Fe 2p3/2) and 723.5 eV (Fe 2p1/2), which
was corrected by the binding energy of C 1s (284.6 eV). It
is in accordance with the +3 oxidation state of iron [27]. In
the case of FeIV(TPFC)Cl, the binding energy for Fe 2p3/2
and Fe 2p1/2 is 710.5 eV and 725.0 eV, respectively. From
FeIII(TPFP)Cl to FeIV(TPFC)Cl, the binding energy of Fe
2p3/2 and Fe 2p1/2 increases by 0.3 eV and 1.5 eV, respec-
tively. This indicates the iron in FeIV(TPFC)Cl is of +4 oxi-
dation state. And this is similar to the previous observation,
in which the Fe 2p3/2 binding energy increased by 0.3 eV
from Fe2+ porphyrin to Fe3+ corrole [28].
Preparation of Fe(TPFC)Cl
TPFC (20 mg, 25 μmol) was dissolved in about 20 mL of
DMF. After adding FeCl2·4H2O (100 mg, 0.5 mmol), the
mixture was heated to refux for 4 h under argon in the dark,
then left to cool. The mixture was extracted with dichlo-
romethane (DCM)/water (1/3 in volume), and the organic
phase was collected and washed four or fve times with dis-
tilled water. The solvent was removed under rotary evapora-
tion to obtain the crude product. Then, the product was puri-
fed by column chromatography using DCM/MeOH (2/98)
and washed with 7% hydrochloric acid. Recrystallization
from DCM/hexane aforded Fe(TPFC)Cl as a brown solid.
Yield 15.1 mg (68%). UV–Vis (CH2Cl2) λmax/nm (log ε):
379 (4.54), 395 (4.58). ESI-HRMS, calcd for C37H8F15FeN4:
848.9854, found for C37H8F15FeN4: 848.9851.
Preparation of Fe(TPFP)Cl
Similar to Fe(TPFC)Cl, Fe(TPFP)Cl was synthesized by
the reaction of TPFP (20 mg, 21 μmol) and FeCl2·4H2O
(100 mg, 0.5 mmol) in the same volume of DMF. The solu-
tion was heated to refux for 6 h in the air. After extraction
with DCM from water several times, the organic phase of
the solution was concentrated under vacuum, and the crude
Fig. 1 UV–visible spectra of
Fe(TPFC)Cl/[Fe(TPFC)]2O (a)
and Fe(TPFP)Cl/[Fe(TPFP)]2O
(b) in CH2Cl2
1 3

Transition Metal Chemistry
Fig. 2 XPS spectra of Fe 2p
from the sample of Fe(TPFC)Cl
(a) and Fe(TPFP)Cl (b)
the catalytic activity. Therefore, we proceeded to explore
their activities as electrocatalysts in HER.
Cyclic voltammetry
The CVs of Fe(TPFC)Cl and Fe(TPFP)Cl in DMF are shown
in Fig. 3. Fe(TPFC)Cl (a) displays three reversible waves
(E1/2) at +0.52 V, −0.57 V and −1.58 V versus Ag/AgNO3,
which we assign to the FeV/IV, FeIV/III and FeIII/II couples.
While the third reduction (Epa = − 1.73 V) is not revers-
ible, according to previous reports [29], which is attributed
to a chemical reaction, a chlorine anion dissociation from
the Fe(II) complex. In Fig. 3b, the CV of Fe(TPFP)Cl also
shows three reversible waves (E1/2) at −0.04 V, −0.86 V and
−1.39 V versus Ag/AgNO3, which can be assigned to the
FeIII/II, FeII/I and FeI/0 couples. As observed in Fig. S1, the
peak current responses on redox reactions of the two com-
plexes both show good linear correlation with the square root
of the scan rate. This phenomenon indicates that the redox
reactions are difusion-controlled processes [30], with elec-
trolyzed complexes freely difusing in solution. To assure
that the complexes are responsible for catalysis instead of the
raw materials for the synthesis reaction, a series of control
experiments were carried out under the same conditions,
including the CVs of TPFC, FeCl2·4H2O, TPFP and the mix-
ture of the free-base and FeCl2·4H2O. As observed in Fig.
S2–S6, the redox waves observed for TPFC, FeCl2·4H2O,
TPFP or the mixture of the free-base and FeCl2·4H2O are
inconsistent with that obtained for Fe(TPFC)Cl or Fe(TPFP)
Cl. This implies that the metal complexes are responsible for
Catalytic hydrogen evolution in acetic acid media
To evaluate their possible electrocatalytic activities and
mechanism for hydrogen evolution, we recorded their CVs
performed under diferent concentrations of acetic acid in
DMF. Figure 4 shows that the peak currents increase in dis-
tinct degree as the concentration of acetic acid increases
from 0 to 12 μM and the onset reduction potential gradually
shifts to more positive values. For Fe(TPFC)Cl (Fig. 4a),
addition of unequal amounts of CH3COOH expands cata-
lytic currents at potentials near the FeII-Cl/FeII couple at a
potential of about −1.73 V versus Ag/AgNO3. This rise in
peak current could be due to the catalytic hydrogen evolution
from acetic acid [30]. According to previous reports [13,
29], we assumed a possible electrocatalytic hydrogen evolu-
tion pathway as shown in Scheme 2a. After losing a chlorine
anion, electro-generated FeII(TPFC) species bonds with a
proton to form (TPFC)FeIII-H intermediate. It might further
undergo bimolecular homogenization to H2 and FeIII(TPFC),
which can rapidly revert to (TPFC)FeIIICl by absorbing Cl−.
As for Fe(TPFC)Cl (Fig. 4b), a new reduction wave was
observed at the potential of − 1.85 V versus Ag/AgNO3
because of the addition of acetic acid. As reported [19,
31], a possible electrocatalytic hydrogen evolution process
Fig. 3 CVs of Fe(TPFC)Cl
(a 942 μM) and Fe(TPFP)
Cl (b 784 μM). Conditions:
0.1 M [n-Bu4N]ClO4 as
supporting electrolyte, scan
rate=100 mV/s, glassy carbon
electrode, Ag/AgNO3 refer-
ence electrode, Pt wire counter
electrode, Ferrocene internal
standard (b, *), r.t
1 3

Transition Metal Chemistry
Fig. 4 CVs of Fe(TPFC)Cl
(a 942 μM) and Fe(TPFP)Cl
(b 784 μM) in the presence
of varying concentrations of
acetic acid in DMF. Condi-
tions: 0.1 M [n-Bu4N]ClO4 as
supporting electrolyte, scan
rate=100 mV/s, glassy carbon
electrode, Ag/AgNO3 refer-
ence electrode, Pt wire counter
electrode, Ferrocene internal
standard (b), r.t
Scheme 2 Possible mechanism
for HER electrocatalyzed by
Fe(TPFC)Cl (a) and Fe(TPFP)
Cl (b)
(a)
(b)
for Fe(TPFC)Cl is shown in Scheme 2b. In the progress of
hydrogen evolution, metal–hydride (TPFP)ClFeI-H inter-
mediate may also exist, formed by the irreversible one-
electron reduction in higher valent metal–hydride (TPFP)
ClFeII-H species (pathway A). Thus, the main catalytic
hydrogen evolution route in the catalytic system should be
pathway A owing to the active iron(I) porphyrin species.
To thoroughly access the electrocatalytic activities of
Fe(TPFC)Cl and Fe(TPFP)Cl, a number of electrolyses
in DMF with acetic acid at regularly changed applied
potential were performed in a double-compartment cell.
Figure 5a, c shows the total charge for 2 min electrolysis
of acid solutions containing Fe(TPFC)Cl and Fe(TPFP)
Cl. The more negative the potential applied, the greater
the charge generated. Moreover, if the catalysis occurs
at a lower overpotential, it could be evaluated as a good
catalyst. The defnition of overpotential is given by Eq. (1)
[32]:
From Fig. 5, for Fe(TPFC)Cl (a), catalysis occurred at the
overpotential of 742 mV versus SHE. Furthermore, during
2 min of electrolysis, the maximum charge achieved 14.39 mC,
more than Fe(TPFP)Cl (only 8.69 mC) at an overpotential of
942 mV versus SHE. According to Eq. (2) [33], at an overpo-
tential of 942 mV versus SHE, the maximum TOF electrocata-
lyzed by Fe(TPFC)Cl, and Fe(TPFP)Cl reached 19.79 h−1 and
14.36 h−1, respectively.
ΔC
TOF =
(2)
F × n1 × n2 × t
where ΔC is the charge from the electrolysis during CPE
experiments (has already deducted the charge of blank solu-
tion), F is the Faraday constant, n1 is the molar number of
electrons required to produce 1 mol of hydrogen, n2 is the
molar number of catalyst in solution and t is the time of
electrolysis.
Overpotential = Applied potential − EH◦ A
(1)
where EH◦ A = E◦
−
⋅ pKa,HA, while E◦ is the stand-
2.303RT
ard potential oHf+the soFlvated proton/hydridHe+ couple, and
K
a,HA is the dissociation constant of acetic acid.
1 3

Transition Metal Chemistry
Fig. 5 Charge buildup versus
time from electrolysis of
Fe(TPFC)Cl (a 2.83 μM),
Fe(TPFP)Cl (c 2.35 μM) in
DMF (0.1 M [n-Bu4N]ClO4)
under various overpotentials.
All data of change have been
processed by blank subtraction.
b, d display TOF for electro-
catalytic hydrogen production
by Fe(TPFC)Cl (2.83 μM) and
Fe(TPFP)Cl (2.35 μM) under
diferent overpotentials (mV
versus SHE), respectively
Faradaic efciency value of 96% for HER (Fig. S10(a)).
Based on Eq. (2), the TOF value for Fe(TPFC)Cl was
274.2 h−1 (Fig. 5b) at an overpotential of 838 mV versus
SHE (Eq. 3).
Catalytic hydrogen evolution in neutral bufer
media
Considering the practicality of Fe(TPFC)Cl, we explored
whether it is electrocatalytically active in aqueous solu-
tion. As shown in Fig. S7 (a), the catalytic current changed
only slightly until the potential of −1.45 V versus Ag/AgCl
when Fe(TPFC)Cl was absent in the neutral solution. With
Fe(TPFC)Cl added gradually, the strength of peak current
increased slowly and the onset reduction potential shifted
positively to −1.38 V versus Ag/AgCl. This indicates that
Fe(TPFC)Cl can also catalyze HER from aqueous solution.
Besides, the maximum currents catalyzed by Fe(TPFC)Cl
are non-innocent with the pH values of bufer solution (Fig.
S8(a)), which disclosed that the catalytic current was con-
trolled by the free difusion of Fe(TPFC)Cl molecules to the
electrode surface. Moreover, the situation of Fe(TPFP)Cl is
similar when the same experiments were conducted.
Overpotential = Applied potential − 0.059 pH
(3)
Compared to Fe(TPFC)Cl, in Fig. 6d, the TOF value for
Fe(TPFP)Cl was 233.1 h−1 at an overpotential of 838 mV
versus SHE (pH 7.0). Analyzed by GC, Fe(TPFP)Cl can pro-
duce 0.11 mL (0.005 mmol) of H2 (Fig. 7b) over electrolysis
for 1 h with Faradaic efciency value of 93% for HER (Fig.
S10(b)). Through the results of these experiments, we found
that Fe(TPFC)Cl is a better catalyst than Fe(TPFP)Cl, not
only in DMF but also in a solvent mixture of acetonitrile
and water. The performance was consistent with outcomes
of the work by Solomon et al. [34], who studied the difer-
ences in energy in the oxidation states between corroles and
porphyrins and the interactions of these compounds with
metals. They showed that there are more accessible states
in corroles, which allows more accessible reduction at the
metal center [35].
To determine that Fe(TPFC)Cl is also an efcient HER
electrocatalyst in neutral bufer solution, CPE experiments
were performed. Figure 6 shows the total charge for 2 min
electrolysis of neutral bufer solution containing Fe(TPFC)
Cl and Fe(TPFP)Cl. When Fe(TPFC)Cl was absent (Fig.
S9), the maximum charge electrolyzed was 322 mC under
− 1.45 V versus Ag/AgCl. However, the charge reached
522 mC because of the addition of Fe(TPFC)Cl, which can
be attributed to the formation of hydrogen. The amount of
evolved hydrogen was analyzed by GC, which gave 0.33 mL
(0.015 mmol) of H2 (Fig. 7a) during 1 h of electrolysis with
Catalytic stability of Fe(TPFC)Cl
To confrm that Fe(TPFC)Cl is able to catalyze hydrogen
evolution continuously, CPE experiments during 3 days
were conducted in the neutral bufer solution. As observed
in Fig. S11, a total charge of 368.6 C was produced during
1 3

Transition Metal Chemistry
Fig. 6 Charge buildup of
Fe(TPFC)Cl (a 2.83 μM),
Fe(TPFP)Cl (c 2.35 μM) versus
a series of applied potentials
in 0.25 M phosphate bufer at
pH 7.0. All data of change have
been background subtracted.
TOF for electrocatalytic hydro-
gen production by Fe(TPFC)
Cl (b 2.83 μM), Fe(TPFP)Cl (d
2.35 μM) was displayed under
diferent overpotentials (mV
vs. SHE) in 0.25 M phosphate
bufer (pH=7.0)
Fig. 7 GC spectra after a 1 h
of CPE experiment at −1.45 V
versus Ag/AgCl of Fe(TPFC)
Cl (a 2.83 μM), Fe(TPFP)Cl (b
2.35 μM) in 0.25 M phosphate
bufer at pH 7.0 and CH4 was
added as standard
the 72 h electrolysis in the presence of Fe(TPFC)Cl at an
applied potential of −1.45 V versus Ag/AgCl, and the cata-
lytic current remained almost constant. After electrolysis
completion, there was no decomposition of Fe(TPFC)Cl in
the electrolytic cell. And the pH value changed from 7.0
to 8.1, consistent with the electrolysis of water to produce
hydrogen, leaving the hydroxide ions enriched around the
electrode.
by TOF value and faradaic efciency in acetic acid or
aqueous media. These two iron tetrapyrrolic macrocycle
complexes display diferent mechanism in the electro-
catalytic hydrogen evolution process. Systematic inves-
tigation on electrocatalytic HER in aqueous solution
using Fe(TPFC)Cl at diferent conditions such as using
additional axial ligands, or tuning the water solubility of
Fe(TPFC)Cl by substituting the para-fuorine with amines
bearing hydroxyl groups or amino acids, is still going on
in our laboratory.
Conclusions
Acknowledgements This research was funded by National Natural Sci-
ence Foundation of China (No. 21671068).
In summary, Fe(TPFC)Cl is proved a potential electro-
catalyst for producing hydrogen using water as the proton
source. Iron corrole Fe(TPFC)Cl exhibited better per-
formance than iron porphyrin Fe(TPFP)Cl as indicated
1 3

Transition Metal Chemistry
19. Zhang D-X, Yuan H-Q, Wang H-H, Ali A, Wen W-H, Xie A-N,
Zhan S-Z, Liu H-Y (2017) Transit Met Chem 42:773–782
20. Wu Y, Rodríguez-López N, Villagrán D (2018) Chem Sci
9:4689–4695
References
1. Liu YR, Du YM, Gao WK, Dong B, Han Y, Wang L (2018) Elec-
trochim Acta 290:339–346
21. Lei H, Fang H, Han Y, Lai W, Fu X, Cao R (2015) ACS Catal
5:5145–5153
2. Lv T, Wu MH, Guo MX, Liu Q, Jia LS (2019) Chem Eng J
356:580–591
22. Levy N, Mahammed A, Friedman A, Gavriel B, Gross Z, Elbaz
L (2016) ChemCatChem 8:2832–2837
3. Dey S, Rana A, Dey SG, Dey A (2013) ACS Catal 3:429–436
4. Solis BH, Maher AG, Honda T, Powers DC, Nocera DG,
Hammes-Schifer S (2014) ACS Catal 4:4516–4526
5. Lubitz W, Ogata H, Rüdiger O, Reijerse E (2014) Chem Rev
114:4081–4148
23. Simkhovich L, Mahammed A, Goldberg I, Gross Z (2001) Chem
Eur J 7:1041–1055
24. Gross Z, Galili N, Saltsman I (1999) Angew Chem Int Ed
38:1427–1429
6. Tard C, Pickett CJ (2009) Chem Rev 109:2245–2274
7. Dempsey JL, Brunschwig BS, Winkler JR, Gray HB (2009) Acc
Chem Res 42:1995–2004
25. Lindsey JS, Wagner RW (1989) J Org Chem 54:828–836
26. Zhang R, Vanover E, Chen T-H, Thompson H (2013) Appl Catal
A Gen 464:95–100
8. Popczun EJ, Read CG, Roske CW, Lewis NS, Schaak RE (2014)
Angew Chem Int Ed 53:5427–5430
27. Ghaleno MR, Ghafari-Moghaddam M, Khajeh M, Oveisi AR,
Bohlooli M (2019) J Colloid Interface Sci 535:214–226
28. Schmid M, Zugermeier M, Herritsch J, Klein BP, Krug CK, Rup-
penthal L, Mueller P, Kothe M, Schweyen P, Broering M, Got-
tfried JM (2018) J Phys Chem C 122(19):10392–10399
29. Fang Y, Ou Z, Kadish KM (2017) Chem Rev 117(4):3377–3419
30. Thoi VS, Karunadasa HI, Surendranath Y, Long JR, Chang CJ
(2012) Energy Environ Sci 5:7762–7770
9. Cao J-P, Fang T, Fu L-Z, Zhou L-L, Zhan S-Z (2014) Int J Hydrog
Energy 39:13972–13978
10. Callejas JF, McEnaney JM, Read CG, Crompton JC, Biacchi AJ,
Popczun EJ, Gordon TR, Lewis NS, Schaak RE (2014) ACS Nano
8:11101–11107
11. Marinescu SC, Winkler JR, Gray HB (2012) Proc Natl Acad Sci
USA 109:15127–15131
31. Alenezi K (2017) Int J Electrochem Sci 12:812–818
32. Felton GAN, Glass RS, Lichtenberger DL, Evans DH (2006) Inorg
Chem 45:9181–9184
12. Bediako DK, Solis BH, Dogutan DK, Roubelakis MM, Maher
AG, Lee CH, Chambers MB, Hammes-Schifer S, Nocera DG
(2014) Proc Natl Acad Sci USA 111:15001–15006
13. Yuan H-Q, Wang H-H, Kandhadi J, Wang H, Zhan S-Z, Liu H-Y
(2017) Appl Organomet Chem. https://doi.org/10.1002/aoc.3773
14. Mondal B, Sengupta K, Rana A, Mahammed A, Botoshansky M,
Dey SG, Gross Z, Dey A (2013) Inorg Chem 52:3381–3387
15. Lei H, Han A, Li F, Zhang M, Han Y, Du P, Lai W, Cao R (2014)
Phys Chem Chem Phys 16:1883–1893
33. Karunadasa HI, Montalvo E, Sun Y, Majda M, Long JR, Chang
CJ (2012) Science 335:698–702
34. Hocking RK, George SD, Gross Z, Walker FA, Hodgson KO,
Hedman B, Solomon EI (2009) Inorg Chem 48:1678–1688
35. Morales Vasquez MA, Hamer M, Neuman NI, Tesio AY, Hunt
A, Bogo H, Calvo EJ, Doctorovich F (2017) ChemCatChem
9:3259–3268
16. Li M, Niu Y, Zhu W, Mack J, Fomo G, Nyokong T, Liang X
(2017) Dyes Pigments 137:523–531
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
17. Musselman BD, Watson JT, Chang CK (1986) Org Mass Spec-
trom 21:215–219
18. Han Y, Fang H, Jing H, Sun H, Lei H, Lai W, Cao R (2016)
Angew Chem Int Ed 55:5457–5462
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